“All human actions have one or more of these seven causes: chance, nature, compulsions, habit, reason, passion and desire.” ~ Aristotle

What is it about SEVEN? The 7-year itch. The seven dwarfs. Seven days of creation. James Bond 007. Almost all animals have 7 cervical vertebrae. 7 is the number of stellar objects in the solar system visible to the naked eye (Sun, Moon, Mars, Jupiter, Mercury, Venus and Saturn.) 7 inches – the original diameter of the 45rpm gramophone record.

For anyone who spends time in corporate meetings, it won’t come as a surprise that decision making effectiveness declines as the size of the group grows. But is there really a magic number? The answer is YES, and the number is 7.

According to to Marcia W. Blenko, Michael C. Mankins, and Paul Rogers, authors of Decide & Deliver: 5 Steps to Breakthrough Performance in Your Organization, once you have 7 people in a decision-making group, each additional person reduces decision effectiveness by 10%.

And really large decision making groups become completely ineffective. According to the research team, a group of 17 or more rarely reaches any decisions.

This resonates with me, and is a predictor of positive “group dynamic” as well. I coach executives, both individually and in groups. Groups smaller than 6 seem to lack the breath of ideas and collaboration. On the other hand, groups larger than 8 become unwieldy, and there is not enough time or focus for each individual to contribute effectively.

If you are forced to work within a decision-making group larger than 7 people, I recommend you break into smaller groups to work through the decision making process. You can then re-assemble as a larger group to finalize the decision. Or, you can parse out different issues to different teams, and have them work simultaneously to reach decisions. Then have the larger group to review and endorse each of the decisions made by the individual teams.

I sent this stat to a colleague who works with Fortune 1000 CEOs and their teams on high-visibility, high-impact projects. Her comment: “It would explain a lot that I knew by experience! I have a client who consistently adds people to his meetings (they sometimes swell to 20 or so), and his customary complaint is that nothing gets decided or moved forward…..DUH.”